During drilling of offshore wells a drill liquid is required. Such drill liquid may be water based or oil based. The drill liquid consists of a mixture of a number of different chemicals and compounds, and several of these ingredients represent a risk for the human being. The chemicals are commonly supplied in sacks of 25-30 kg and the content of the sacks is fed into a mixer and mixed into a circulating drill fluid. The drill fluid has to be tailor made to the specific requirements at any time, the need for different mixtures often being changed. On this basis it is thus required that the mixing of the drill liquid is executed on the platform as an integral part of the drilling operation.
The problem to be solved is thus how to cut up the sacks and empty these in order to mix the content of the sacks into the circulating drill liquid in a most efficient manner. Such mixing should, amongst other due to the health hazards, but also from an economical point of view, be automatic and without representing a health risk for the operator.
A large number of different machines, performing such operations, are already available on the market.
U.S. Pat. No. 4,930,968 describes a sack cutting machine comprising a unit for cutting up the sack so that the powder inside may be released, a first transporting screw for transport of the powder and the sack; a drum for separating the powder from the sack, the first transport screw being concentrically arranged in the drum; a feeding screw arranged below the drum and in open communication with the drum for transport of the powder to a separate location and a means for collecting ripped, empty sacks, arranged at the opposite side of the drum and said first feeding screw, seen with respect to the feeding opening for filled sacks. According to this solution an intact sack with its powder content is fed into the machine at the end of the sack cutting means, whereupon the sack by means of the first transporting screw is moved in a direction towards a stopper whereby the sack is cut and the content released, whereupon the direction of rotation is reversed.
EP 1 123 868 describes a sack cutting machine in the form of a feeding screw, arranged in a tray, provided with fixed knives for cutting the sack, and a drum arranged at one end of the feeding screw, the content being separated from the sack in said drum. At the opposite end an opening directing towards a tray for collection of empty sacks is arranged.